The present invention relates to distributed antenna systems such as may be common in mobile communication networks.
Mobile terminals have become ubiquitous in modern society. Cellular phones, personal digital assistants, pagers, and the like, all occupy important niches within our daily existence. Mobile terminals allow individuals to access communication networks without the need for a land-based line. Thus, the individual may communicate while traveling across the country, or even just down the hall, away from a normal phone.
With the explosion of the popularity of mobile terminals, many companies have set up internal local area phone networks that may interface with the Public Land Mobile Network (PLMN) or may, in fact, be part of the PLMN. These internal phone networks may be proprietary or public and are designed to take advantage of the mobile terminals in the possession of employees or individuals at the location. In some instances, individuals present in areas covered by these internal networks intend to use their mobile terminals in place of a normal desk phone. This may eliminate wiring concerns in the building as well as promote easy growth. Other reasons may also exist for these internal networks.
These internal local area phone networks are characterized frequently by the use of distributed antenna systems that improve coverage throughout a building or other location. These distributed antenna systems, at least in the mobile terminal context, are characterized by one or more base stations each having a plurality of antennas connected thereto, usually by a coaxial line. Normally, a single antenna would experience local nulls and other interference that would preclude a single cell from adequately serving a building. The use of a distributed antenna system is designed to reduce structural interference to a minimum and offset other factors, which may contribute to poor coverage. Distributed antenna systems may, of course, be used for other reasons.
One shortcoming for these existing distributed antenna systems is that every antenna receives and transmits on every channel in use by the system. Thus, there may not be any reuse of channels in a distributed antenna system, even for those systems with multiple base stations, where channel reuse may be more feasible. Because every antenna uses every channel, there is no provision to allow an antenna to transmit a subset of the total available channels. Without allowing selected transmission, there is no ability for dynamic channel allocation.
In short, there is no ability in the present systems to create virtual cells associated with each antenna in a distributed antenna system. Such virtual cells would allow channel reuse, enabling more users to be active at the same. Further, such virtual cells may benefit from dynamic channel allocation wherein an antenna experiencing a heavy usage cycle could use additional channels, while antennas experiencing lulls may relinquish channels. Thus, there remains a need for the ability to tune selected antennas within a distributed antenna system to selected channels.
The problems associated with the prior art may be solved by using one or more tunable filters with the transmitter portion of each antenna in a distributed antenna system. The tunable filters may have multiple pass bands allowing a plurality of channels to be transmitted. In this manner, the transmit channels of each antenna within the distributed system may be controlled remotely and dynamically reassigned as needed or desired. Control information may originate at a base station and be directed down a coaxial line to the filters with instructions about to which channels a particular antenna should tune. As usage varies amongst the antennas, more channels may be dynamically reassigned to antennas experiencing heavy loads.